1. Field of the Invention
The present invention relates to a system and tyre for the continuous determination of the interaction between a tyre and the ground during the movement of a motor vehicle.
The present invention also relates to a method for the continuous determination of the behaviour of a tyre, and of the vehicle equipped with the said tyre, as it moves along the road.
More particularly, the present invention relates to methods for detecting an interaction between at least one moving tyre and a contact surface; for detecting the behaviour of at least one tyre moving with respect to a contact surface; for enabling a tyre to generate and transmit a signal descriptive of its own behaviour when moving with respect to a contact surface; for enabling a tyre mounted on a wheel rim to generate a signal descriptive of its own behaviour when moving with respect to a contact surface; for manufacturing a wheel inclusive of a tyre, rim and sensor, that is capable of generating a signal descriptive of the behaviour of the tyre when moving with respect to a contact surface; for monitoring the behaviour of a moving vehicle mounted on wheels; for controlling the behaviour of a moving vehicle mounted on wheels; for quantifying the magnitude of an event caused by an interaction between at least one moving tyre and a contact surface; for monitoring the structural uniformity of a tyre; and for detecting deflation of a tyre.
The present invention also relates to:                a kit for detecting the behaviour of a tyre mounted on a rim and moving with respect to a contact surface,        a vehicle wheel that includes tyre, rim and device for detecting the behaviour of the tyre moving with respect to a contact surface, and        a vehicle that includes body, suspension, at least one wheel fitted with a tyre and optionally at least one device for controlling the behaviour of the moving vehicle.        
2. Description of the Related Art
During the movement of a motor vehicle, a knowledge of the operating conditions of a tyre makes it possible to determine the actions to be taken to control and regulate the behaviour of the motor vehicle. In particular, it is useful to know the condition of skidding or absence of skidding of the tyre and the variation of the available adhesion with respect to a reference condition, in order to activate, for example, devices to prevent brake locking (antiskid or ABS devices), devices to prevent skidding in acceleration, active suspension, etc.
It is a known practice in the state of the art to use systems designed to detect the interaction between a tyre moving on a given contact surface and the surface itself in order to extract information about the behaviour of the tyre and/or about a particular condition of operation of a tyre and, more generally, about the behaviour of a vehicle fitted with this tyre.
Of these systems, one type comprises systems based on the use of sensors that supply continuous signals representing the values of particular parameters of the tyre, such as sensors of pressure, of temperature and of localized deformation.
This type includes the extensometers, that is so-called strain gage sensors, e.g. prismatic elements of a piezoelectric or magnetic polymer inserted into the tread of the tyre to detect localized deformations of the tread in the footprint.
EP-B1-0 444 109 describes a method for controlling the movement of a motor vehicle provided with tyres which interact with the ground to form corresponding footprints, comprising the steps of                monitoring the behaviour of the footprints and generating at least one corresponding footprint signal indicating the behaviour of the footprint, and        using at least one footprint signal to monitor the movement of the motor vehicle,        detecting at least one driving control signal generated by the driver of the motor vehicle, and        processing at least one driving control signal in dependence on at least one footprint signal in order to control the movement of the motor vehicle.        
To detect this behaviour of the footprints, this method makes use of piezoelectric extensometers embedded in the tread strip because they have to detect the deformations in the footprint. This causes significant disadvantages both in the construction of such a tyre and in the measurement of the deformations.
This is because piezoelectric extensometers are formed from piezoresistive rubber strips, and a piezoelectric or piezoresistive rubber is not an elastomer, but a plastic material, and therefore gives rise to problems of compatibility with the rubber of the tread (because of the different moduli and different adhesion capacities) as well as problems of fastening.
The applicant has also observed that the aforesaid method detects only the deformations of the tread strip within the footprint, so that all other deformations occurring in a moving tyre are disregarded. Finally, the applicant has also observed that the deformations of the footprint cannot be correlated in a one-to-one way with the deformations of the tyre.
Similarly the prior art includes systems designed to obtain specific information on the behaviour and/or condition of the tyre, such as to describe the overall situation of the complete tyre rather than, as is typical of the aforementioned detection systems, of a localized portion of the tyre.
For example, U.S. Pat. No. 5,913,240 relates to a device capable of detecting the longitudinal force acting on a vehicle tyre caused by the torsional deformation of the tyre itself, in order to control tyre slip due to a positive or negative acceleration of the vehicle. According to this patent the determination of this longitudinal force can also be used to monitor the inflation pressure of the tyre. The device has a supporting structure integral with the vehicle's brake calliper and comprises at least one pair of sensors arranged radially in fixed positions, one on the outside and the other on the inside, i.e. at a greater and at a shorter distance from the axis of rotation of the wheel. On the side facing the vehicle the wheel is fitted with at least one pair of position marks, a radially outer mark and a radially inner mark, at different distances from the axis of rotation. The passing of these marks is detected by the said sensors which measure, in the period of time lapsing between their passage, the torsional deformation of the tyre, from which, as indicated, the longitudinal force acting on the tyre can be calculated. The signals obtained by this means are sent to a processing unit which warns the driver of the vehicle if the tyre is in a condition of slip and, optionally, also of the state of inflation of the tyre.
A different type of detection system comprises systems based on the use of sensors that supply discontinuous cyclical signals representative of particular events during the running of the tyre, such as, for example sensors that indicate when they enter and/or leave the footprint of the tyre.
EP-A1-0 887 211 describes a tyre monitoring system comprising a sensor located within the tyre and enabled to create an electrical pulse when the said sensor passes through the footprint formed by the contact of the tyre with the ground during rolling. The system of this patent application also comprises means for determining the ratio of the said electrical pulse to the duration of one revolution of the tyre and means for transmitting the said ratio to a processing unit within the vehicle.
In particular, the sensor is a deformation indicator, for example an extensometer, possibly made from piezoelectric material, located within the tyre in such a way that the said electrical pulse has a first peak at the point when the sensor enters the footprint and a second peak at the point of exit from the footprint. The sensor therefore detects the instant of entry into the footprint and the instant of exit from this area, and, according to the teaching of this patent, the ratio between the time elapsed between the two peaks and the time of a complete revolution of the tyre can be used to determine the flattening of the tyre during the movement of the vehicle. This is because, if the angular velocity of the tyre and its radius are known, it is possible to measure the length of the footprint. The length of the footprint is therefore related to the flattening of the tyre, which is a critical parameter of the tyre in operation, particularly in tyres for heavy goods vehicles.
Another type of detection system comprises systems based on the use of a sensor that supplies a cyclical and continuous signal about the behaviour of a single point of the moving tyre. This sensor is typically an accelerometer.
A plurality of the said sensors are attached to individual separate points on the tyre, and the abovementioned systems are designed to work out the behaviour of a tyre and/or of a vehicle from the description of the movement in space and time of the said points.
Each of the said sensors supplies a signal which is cyclical, in the sense that it repeats itself at each revolution of the tyre, is continuous in time and is descriptive of the movement of the single point to which the sensor is attached.
The data acquired by the abovementioned system are claimed to be useful for intervening on the motor vehicle's controls (ABS, active suspensions, etc.) and modifying its behaviour, e.g. during braking, accelerating, skidding and the like.
U.S. Pat. No. 5,825,286 relates to a system and method for extracting data relating to a vehicle comprising the following steps:                detecting parameters regarding the behaviour of the vehicle from the inside of a tyre mounted on the vehicle wheel,        digitizing the said data inside the tyre and transmitting them out of the tyre at predetermined intervals,        shortening these predetermined intervals if the parameters change by a predetermined percentage,        receiving these data at a point external to the tyre,        comparing these data with preset values for each of the said parameters,        showing the said data, and        activating an alarm when these data, for each of the said parameters, exceed a preset limit        
One of the sensors for detecting the said parameters is a vibration sensor which can be a piezoelectric element, of undefined type, which emits an electrical voltage signal as its impedance varies (col. 12, lines 26–29). All the sensors form part of a module fitted to each wheel. The Applicant has observed that the abovementioned method similarly requires the acquisition of information from separate points of the tyre.